1. Field of the Invention
The present invention relates to a torque measuring apparatus for measuring friction torque produced when the direction of a front wheel of an automobile is changed, and a rotation center measuring apparatus for measuring the rotation center of a front wheel of an automobile when its direction is changed.
2. Description of the Related Art
An automobile has a steering wheel and the traveling direction of the automobile is freely changed in accordance with the line of a road by the driver handling the steering wheel. As is generally known, when the steering wheel is handled, the direction of front wheels is changed in accordance with how the steering wheel is handled to change the traveling direction.
Accordingly, a channel inside the automobile that connects between the steering wheel and the front wheels has a transmission mechanism for changing the direction of the front wheels in conjunction with handling of the steering wheel. Since this transmission mechanism is mainly composed of connecting parts such as gears, the direction of wheels cannot be changed unless the steering wheel is operated with operation torque comparable to friction and the like intrinsic to the transmission mechanism. The larger the friction, greater operation torque is required and handling of the steering wheel becomes more difficult.
Accordingly, a recent automobile is provided with a power steering device in the transmission mechanism for reducing operation torque so as to provide ease of operation to drivers (reference may be made to Japanese Patent Laid-Opens No. 05-229439 and No. 2003-81119, for example).
By the way, since the friction torque and/or hysteresis characteristic (difference between leftward and rightward steering) of a steering system (from the steering wheel to wheels) of an automobile largely affects the operability of the vehicle and the feel of handling of the steering wheel, they need to be accurately measured also for management of dispersions among individual automobiles and/or trends specific to individual models (flavoring) and the like.
FIG. 1 is a view showing a configuration of a measuring apparatus for measuring friction torque and a result of measurement. Part (a) of FIG. 1 shows the configuration of the measuring apparatus, and Part (b) of FIG. 1 shows the friction torque measured by the apparatus for each steering angle in the form of hysteresis characteristic according to the difference between leftward and rightward steering.
The configuration of the measuring apparatus will be first described with reference to Part (a) of FIG. 1.
As illustrated in the lower portion of Part (a) of FIG. 1, a front wheel 10 of an automobile 1 is placed on a turntable 30.
As illustrated in the upper portion of Part (a) of FIG. 1, an arm 31 extends from the turntable 30 with its one end fixed on the turntable, and at the other end of the extending arm 31, an operation bar 32 is provided in a direction orthogonal to the direction in which the arm 31 extends. By manually pushing and pulling the operation bar 32, it is possible to rotate the turntable 30 on which one end of the arm 31 is fixed.
At the end of the operation bar 32 on the manual operation side, there is provided a load meter 33 for measuring force while the turntable 30 is rotated by pushing and pulling the operation bar 32. At the center of the turntable 30, an angle detector 34 is provided so that measurement of the rotation angle may be measured while the turntable 30 is rotated.
Consequently, when the front wheel 10 on the turntable 30 is being rotated by pushing and pulling the operation bar 32 on the side of the load meter 33 with a hand, the force required for rotation is measured by the load meter 33 and also the rotation angle of the turntable 30 while it is being rotated by pushing and pulling the operation bar is measured by the angle detector 34 as the rotation angle of the front wheel 10. Since the length of the arm 31 shown in Part (a) of FIG. 1 is a known value, friction torque Tt can be determined for each rotation angle based on the force measured by the load meter and rotation angle θt detected by the angle detector 34. Thus, the locus of friction torque for each rotation angle in accordance with the direction of rotational operation is determined in the form of hysteresis characteristic as shown in Part (b) of FIG. 1. Part (b) of FIG. 1 shows in the form of hysteresis characteristic how friction torque changes according to the difference between leftward and rightward steering, with the lateral axis representing the rotation angle θt of the turntable and the longitudinal axis representing friction torque Tt determined from computation.
As will be seen from the configuration of Part (a) of FIG. 1, however, because the rotation center O of the wheel 10 is different from that of the turntable 30 (i.e., where the angle detector 34 is positioned), friction torque inherent in the transmission mechanism of the steering system provided in an automobile cannot be accurately determined by calculating friction torque from the rotation angle of the turntable when the front wheel 10 is fixed on the turntable 30 and is rotated with it and force measured by the load meter 33.
To resolve this, the front wheel 10 may be placed and rotated on a lifting table while moving the lifting table so that the rotation angle is detected at the rotation center of the front wheels, not the rotation center of the turntable. However, when the wheel is rotated with the lifting table, the lifting table moves along with the rotation of the front wheel due to constraint of the transmission mechanism of the steering system, thus it becomes difficult to determine the rotation center of the wheel. Friction torque cannot be accurately determined unless the rotation angle of the front wheel is determined.